1. Field of the Invention
The invention relates generally to a method of manufacturing a dual gate CMOS transistor of a semiconductor device. More particularly, the present invention relates to a method of manufacturing a CMOS transistor by which ion implantation process is selectively performed to the gate formed region of a polysilicon film after a NMOS transistor region and a PMOS transistor region are defined in the process of manufacturing a CMOS transistor, thus it can obtain a reliable device by solving the problem occurring when polysilicon films doped with different impurities are simultaneously etched and the problem that a tungsten film is oxidized due to a selective oxidization process after forming a tungsten gate electrode.
1. Description of the Prior Art
Referring now to FIGS. 1A through 1C, a method of manufacturing a conventional CMOS transistor will be explained below.
First, referring to FIG. 1A, a trench is formed at a given region on a semiconductor device 101. Then, a device separation film 102 is formed by oxidization process to separate a p-well region and an n-well region. Then, a NMOS transistor region and a PMOS transistor region are defined by means of ion implantation process using an ion implantation mask. Next, a gate oxide film 103 and a polysilicon film 104 are formed on the entire structure. By performing twice application process of a photosensitive film and patterning process, n-type impurity is implanted into the polysilicon film 104 of the NMOS transistor region and p-type impurity is implanted into the polysilicon film 104 of the PMOS transistor region, thus forming a dual polysilicon film.
As shown in FIG. 1B, after the photosensitive film pattern 105 is removed, a barrier metal layer 106, a metal layer 107 and a nitride film 108 are sequentially formed on the entire structure. Tungsten is usually used as the metal layer 107.
Referring now to FIG. 1C, selected regions of the nitride film 108, the metal layer 107, the barrier metal layer 106 and the polysilicon film 104 are etched to form a gate electrode. Then, a oxide film 109 is formed from the side wall of the polysilicon film 104 to the upper portion of the semiconductor substrate 101 by means of a selective oxidization process, so that the tungsten film used as the metal layer 107 is not oxidized. Next, after low concentration impurity ion implantation process, a conventional method of manufacturing a CMOS is performed.
However, in the conventional CMOS manufacturing process as explained above, the gate forming method has a problem of an abnormal oxidization phenomenon in which the metal layer (tungsten film) is expanded due to a subsequent process. This causes a problem that after forming a gate electrode, ions are not implanted into the edge of the gate electrode by the expanded portion of the gate electrode due to abnormal oxidization, in the a low concentration impurity ion implantation process being a subsequent process.
Also, in the conventional dual gate process, upon etching of the polysilicon film for forming the gate electrode, as impurities implanted into the polysilicon film of the NMOS transistor region and the PMOS transistor region are different each other, the etching rate are thus different. Accordingly, it causes a problem that the semiconductor substrate will be damaged, etc. Further, in order to prevent oxidization of tungsten used as the gate electrode, it has to use very expensive equipment only for use in selective oxidization process.